This invention relates to a thermoelectric heat exchange apparatus and, more particularly, to an apparatus for thermoelectrically cooling a system in order to maximize the differential of temperature with minimum energy expenditure, particularly for applications requiring portability.
Thermoelectric systems generally comprise an insulated chamber having an interface to one side of a Peltier thermoelectric device and an interface on the other side of the Peltier device to a heat exchanger with the ambient environment. Peltier devices can operate either as heaters or coolers or even in the presence of an established differential of temperature operate as a means for generating DC electricity. In the application of interest herein, the Peltier device is used either as a heater or cooler.
There are many applications for thermoelectric heat exchanges which place a premium on efficiency and portability. There are, for example, portable ice or refrigeration chests, refrigerated or heated bottles, ice cream and other serving machines, icemakers, water chillers, microcooling applications such as spot cooling in electronics, instrument environments, calibration environments, medical transport chambers and even serving carts for hotels and restaurants. Thermoelectrics are advantageous under circumstances where precise temperature control is an objective.
Thermoelectric cooling devices are also particularly advantageous in environments where the elimination of CFC's is an objective, since thermoelectrics do not require the use of expansion gasses to produce the cooling effect.
One conventional design of the thermoelectric ambient interface is the use of a finned extender block whereby ambient air cools the finned block by convection. This type of cooling is relatively inefficient in that it is difficult to exhaust large quantities of heat rapidly and thereby establish a large temperature differential with adequate heat pumping. The application of power through a thermoelectric device is a function of the desired heat pump effect and differential of temperature. It is therefore highly desirable to exhaust as much excess heat in the cooling system as possible to maximize the temperature differential while handling the heat load. In this manner, the electric power expenditure can also be minimized.
Thermoelectric cooling systems using liquid as a heat exchange medium are known. For example, U.S. Pat. No. 4,744,220 to James M. Kerner and others, issued May 17, 1988, describes a thermoelectric heating and/or cooling system by using liquid for heat exchange in which the application is an insulated reservoir of drinking water wherein heat is pumped from a thermoelectric module by thin sheets of water flowing across the heated cooling block of the thermoelectric device. As described therein, the cooling liquid is assumed to be an infinite supply from an ambient source. Such a source would be a domestic water supply. A related U.S. Patent to Kerner, et al. '220, is U.S. Pat. No. 4,833,888 issued May 30, 1989.
One of the drawbacks of the use of thin sheets of water for cooling in the systems described therein is substantial back pressure requiring that a pump of significant power be used to force the cooling liquid to flow through the cooling block. As a consequence, there may well be a substantial and possibly an excessive expenditure of electric power to drive the pump.
What is needed is a thermoelectric heat exchanger which is efficient in operation and does not expend excessive amounts of power or expend cooling fluid and yet which is capable of quickly exchanging heat with the thermoelectric device to maintain high heat pumping efficiency and high temperature differentials.
A number of patents have been uncovered in a search of the prior art of the U.S. Patent and Trademark Office.
______________________________________ Inventor U.S. Pat. No. Issue Date ______________________________________ Malek et al. 2,456,070 December 14, 1948 Newton 3,255,593 June 14, 1966 Morales 3,240,261 March 16, 1966 Belton, Jr. et al. 2,949,014 August 16, 1960 Hirschhorn 3,154,926 September 25, 1962 Milligan et al. 3,216,204 November 9, 1965 Ogushi et al. 4,576,009 March 18, 1986 Ross 3,400,543 September 10, 1968 Kueckens et al. 3,139,734 July 7, 1964 Levit 2,931,188 April 5, 1960 Lopp et al. 2,928,253 March 15, 1960 Alkenkirch et al. 1,120,781 December 15, 1914 ______________________________________
The Malek et al. patent describes a thermoelectric device wherein hot junctions are cooled by immersion in a bath of liquid contained in a container. Rather than the liquid flowing past the hot junction, the liquid is heated to a vapor or steam phase and the vapor is passed through a conduit to a condenser. Ambient air cools the condenser so that the vapor is condensed to the liquid phase and returned to the container. The condenser may be a radiator type. The Malek invention is a system wherein a phase change is contemplated to effect cooling.
The Newton patent describes a thermoelectric module which is cooled by means of a liquid cooled heat exchanger with a recirculating pump wherein the liquid is circulated through a cooling tower which is intended to exhaust to the open atmosphere. The system is not truly a closed system and expects a certain amount of loss of coolant to the atmosphere through evaporation, which has to be made up and makes it totally unsuitable for a portable system.
The Morales patent discloses a closed-loop system for cooling thermoelectric modules wherein a pump circulates fluid to a liquid-to-liquid heat exchanger wherein in the secondary loop, the cooling water is used only once. This system does not resolve the basic problem of eliminating the excessive waste of water.
The Belton, Jr. et al. patent describes a thermoelectric air conditioning apparatus wherein secondary cooling is achieved by a water tower having water sprays in a system basically similar to the Morales device. This is not a truly closed-loop liquid cooling system.
The Hirschhorn patent describes a closed-loop type of system wherein the thermoelectric modules are cooled in a bath of liquid. A pump is used to circulate liquids through tubes having conductive wires therebetween. The purpose is a cooling blanket used to cool bodies in connection with surgical operations.
The Milligan et al. patent shows various embodiments of thermoelectric cooling devices for cooling a chamber, one of which is a closed-loop cooling system which includes a refrigerating fluid in contact with fins of a thermoelectric module. In this system, fluid is vaporized by heat from the fins and is passed through a conduit into a condenser where it is convectively air-cooled and flows by gravity back to an evaporator.
The Ogushi et al., patent describes a closed-loop system that uses both gas and liquid within a loop. Heat is absorbed in a liquid heat-receiving portion to form a gas or vapor, and the gas is directed to a heat-radiating portion having a fan to expedite cooling. Gas condenses to liquid and is directed to an accumulator on opposite sides of a thermoelectric module.
The Ross patent describes a system for cooling power devices of semi-conductor material which generate heat as a result of application of electrical power. In this system there is no provision for addressing the problem of energy efficiency. Further, it is not applicable to the special structures of thermoelectric coolers.
The Kueckens et al. patent describes a system for controlling Peltier elements in which the Peltier elements are described as batteries and in which one side of the Peltier element is immersed in a cooling liquid in an open container.
The Levit patent describes a Peltier device-based fluid cooling system which recirculates water to be cooled as a cooling fluid in an open-loop system. The system relies on heat radiators formed by finned pipes for ultimate heat exchange. The system is not closed.
The Lopp patent describes a thermoelectric cooler or heater for heating and cooling separate bodies of fluids.
The Alkenkirch et al., patent describes an early thermoelectric heating and cooling structure.